Protection induced by commercially available live-attenuated and recombinant viral vector vaccines against infectious laryngotracheitis virus in broiler chickens

Abstract

Viral vector vaccines using fowl poxvirus (FPV) and herpesvirus of turkey (HVT) as vectors and carrying infectious laryngotracheitis virus (ILTV) genes are commercially available to the poultry industry in the USA. Different sectors of the broiler industry have used these vaccines in ovo or subcutaneously, achieving variable results. The objective of the present study was to determine the efficacy of protection induced by viral vector vaccines as compared with live-attenuated ILTV vaccines. The HVT-LT vaccine was more effective than the FPV-LT vaccine in mitigating the disease and reducing levels of challenge virus when applied in ovo or subcutaneously, particularly when the challenge was performed at 57 days rather than 35 days of age. While the FPV-LT vaccine mitigated clinical signs more effectively when administered subcutaneously than in ovo, it did not reduce the concentration of challenge virus in the trachea by either application route. Detection of antibodies against ILTV glycoproteins expressed by the viral vectors was a useful criterion to assess the immunogenicity of the vectors. The presence of glycoprotein I antibodies detected pre-challenge and post challenge in chickens vaccinated with HVT-LT indicated that the vaccine induced a robust antibody response, which was paralleled by significant reduction of clinical signs. The chicken embryo origin vaccine provided optimal protection by significantly mitigating the disease and reducing the challenge virus in chickens vaccinated via eye drop. The viral vector vaccines, applied in ovo and subcutaneously, provided partial protection, reducing to some degree clinical signs, and challenge VIRUS replication in the trachea.

Epidemiology of Avian Infectious Laryngotracheitis with Special Focus to South America: an update

“…In recent years, recombinant vaccines are available in the market, and include the insertion of ILT viral glycoproteins into viral vectors, such as poxvirus (FPV) (Davison et al, 2006) and turkey herpesvirus (HVT) (Vagnozzi et al, 2012). A recombinant fowl pox vaccine, containing the gene encoding the glycoprotein B (gB), was shown to protect chickens against virulent ILTV strains (Tong et al, 2011).…”

Molecular epidemiology of infectious laryngotracheitis: a review

“…In addition, they can be administered in ovo without a negative impact on production performance (Johnson et al, 2010). Recent studies suggest that although these vaccines reduce clinical signs, they do not reduce challenge virus loads in the trachea as live attenuated vaccines do (Johnson et al, 2010;Vagnozzi et al, 2012). Dark purple regions with a grid pattern indicate countries where ILT cases have been documented for longer than 10 years.…”

Attenuation and protection efficacy of ORF C gene-deleted recombinant of infectious laryngotracheitis virus

“…Experimentally it has been demonstrated that although recombinant viral vectored vaccines do reduce clinical signs of the disease, they fail to prevent viral shedding. On the other hand, live-attenuated vaccines are more efficacious in reducing clinical signs and viral shedding (Johnson, et al, 2010;Vagnozzi et al, 2012a) but can still transmit from vaccinated to non-vaccinated chickens (Rodriguez et al, 2007). It has been speculated that incomplete en mass vaccination, particularly with CEO vaccines, results in long-term persistence of selective vaccine subpopulations (García & Riblet, 2001;García et al, 2013b).…”

“…These strains were attenuated by serial passages in either embryonated chicken eggs (chicken embryo origin, CEO) or in chicken tissue culture (tissue culture origin, TCO) (Gelenczei & Marty, 1965;Samberg & Aronovici, 1969). Viral vector vaccines expressing ILTV glycoproteins in turkey herpesvirus (HVT) and fowlpox virus (FPV) (Davison et al, 2006;Johnson et al, 2010;Tong et al, 2001;Vagnozzi et al, 2012a) are commercially available. The hallmark of these recombinant vaccines is their safety, as they do not transmit from vaccinated to non-vaccinated chickens (Armour & García, 2014).…”

“…The remaining 75 chickens were mock-inoculated with tissue culture media. Clinical signs were scored from days 4 to 7 post-inoculation as previously described by Vagnozzi et al (2012a). At 6 days post-inoculation, tracheal swabs were collected from each group of chickens and analysed by real-time PCR to determine trachea virus load.…”